Flexural Bracing Requirements in Axially Loaded Cold-Formed Steel-Framed Walls

This paper explores an all-steel design philosophy for flexural bracing requirements in cold-formed steel stud walls that employ mechanical bridging alone without sheathing. The current cold-formed steel design specification requires the brace for a single compression member to have stiffness equal to twice the ideal brace stiffness, but related proposals for braces in multiple stud walls, including brace force accumulation and minimum brace stiffness, have not yet been adopted. Bracing strength and stiffness demands in cold-formed steel-framed walls must be adequate to ensure safety but not overly conservative so that the requirements cannot be practically met. Elastic critical load and second-order elastic analyses are conducted herein to determine an adequate level of stiffness for a single braced compression member and relationships between strength and stiffness for braced multiple studs to that of a single stud. Statistics of measured member imperfections are incorporated to provide an equivalent imperfection for multiple stud walls. Design by second-order analysis is utilized to determine how alternating the direction of studs affects strength and stiffness requirements. For a single-braced compression member, the impact of allowing a minimum of 1.33 times, instead of twice the ideal brace stiffness, is explored as an alternative to current requirements. New design expressions for brace stiffness and strength, incorporating the notion of a minimum brace stiffness, and the equivalent imperfection are provided. The new expressions provide the designer with greater flexibility in developing solutions that meet the necessary stiffness and strength requirements.